1. Field of the Invention
The present invention relates to a wire-cut electric discharge machining method capable of preventing damage which is attributable to a shortage of wire supply in the course of machining, and entails lowering of product quality.
2. Description of the Related Art
Electric discharge machining is effected along various machining paths, whose sections are generally composed of a series of machining sections each in the form of a straight line, circular arc or the like. A wire electrode (hereinafter referred to as wire) sometimes may be used up during such electric discharge machining. In such a case, the electric discharge machining must be interrupted, and the interruption of the machining may cause the machined surface of a workpiece to be damaged. Damage caused when the machining is interrupted in the middle of a certain machining section, in particular, is so conspicuous that it lowers the quality of products. For example, if the wire is used up at an intermediate point Ps of, e.g., a fourth section, during the execution of electric discharge machining along a rectangular machining path composed of first, second, third, fourth, fifth, and sixth linear sections POP1, P1P2, P2P3, P3P4, P4P5, and P5P1 shown in FIG. 5, damage is liable to be caused at the machining interruption position Ps.
In order to eliminate such an awkward situation, a proposal has conventionally been made such that the feasible machining time or machining distance should be periodically obtained and displayed in accordance with the wire remaining on a wire supply reel (see Japanese Provisional Patent Publication No. 61-95828, for example). According to the prior art of this type, however, an operator must replace the wire supply reel at a suitable point of time, while observing the machinable time or machinable distance. If the operator fails to monitor the machinable time or machinable distance, therefore, the wire will be used up in the middle of the machining section, e.g., at the intermediate point Ps of FIG. 5, thus entailing the aforementioned awkward situation.